Solar Concentration System With Micro-Mirror Array

ABSTRACT

A solar concentration system including at least one receiver and an array of micro-mirrors connected to a substrate, each micro-mirror of the array being articulateable relative to the substrate, wherein the receiver is positioned relative to the array such that the array directs incoming light to the receiver.

PRIORITY

This application claims priority from U.S. Ser. No. 61/148,488 filed on Jan. 30, 2009, the entire contents of which are incorporated herein by reference.

FIELD

The present patent application relates to solar concentration systems and, more particularly, to solar concentration systems employing micro-mirror arrays for concentrating solar energy onto receivers.

BACKGROUND

Solar concentration systems, also known as solar concentrators, generally operate by focusing a wide area of sunlight into a single point or line using lenses (e.g., Fresnel lenses), mirrors (e.g., parabolic mirrors) or the like. A receiver (or multiple receivers), such as a photovoltaic receiver or a solar thermal receiver, is positioned to receive the concentrated sunlight and generate electrical energy or perform work. In one typical example, the receiver may include one or more photovoltaic cells that convert the concentrated sunlight into electrical energy. In another typical example, the receiver may include a liquid that is heated by the concentrated sunlight, wherein the heated liquid may be used to generate electrical energy or to perform work (e.g., move a piston).

Efficient operation of a solar concentration system typically requires proper alignment of the optical elements with the sun such that the sun's energy remains focused on the receiver. Therefore, solar concentration systems typically are mounted on solar trackers that rotate the solar concentration system such that the optical elements remain aligned with the sun as the sun moves across the sky.

Solar trackers typically use motors and gear trains to adjust the position of the solar concentration system relative to the sun. Unfortunately, the use of motors and gear trains substantially increases the overall weight of the system and introduces reliability issues (e.g., frequent maintenance). As such, conventional solar trackers are of little utility in aeronautical and astronautical (e.g., satellites, interplanetary vehicles, lunar bases and planetary bases) applications, wherein the overall weight of the system is of great concern and long-term operational life is required.

Accordingly, there is a need for a solar concentration system that maintains alignment of the optical elements with the receivers as the sun moves across the sky and/or the platform supporting the solar concentration system moves, without introducing the substantial weight and reliability issues associated with typical solar trackers.

SUMMARY

In one aspect, the disclosed solar concentration system may include at least one receiver and an array of micro-mirrors connected to a substrate, each micro-mirror of the array being articulateable relative to the substrate, wherein the receiver is positioned relative to the array such that the array directs incoming solar energy to the receiver.

Thus, the disclosed solar concentration system includes micro-mirrors that articulate relative to the substrate supporting the micro-mirrors, as opposed to articulating the entire substrate. However, optionally, the substrate supporting the micro-mirrors may also be articulated.

In another aspect, the disclosed solar concentration system may include at least one receiver, the receiver including at least one photovoltaic cell, a substrate having a concave surface, wherein the substrate is essentially stationary relative to the receiver, and an array of micro-mirrors disposed on the concave surface, the array including at least 1000 micro-mirrors per square foot of the concave surface, wherein each micro-mirror of the array is articulateable relative to the substrate to direct incoming sunlight to the receiver.

In another aspect, the disclosed solar concentration system may include an array of micro-mirrors connected to a substrate, each micro-mirror of the array being articulateable relative to the substrate, at least one receiver, the receiver being positioned relative to the array such that the array directs incoming light from a light source to the receiver, and a controller configured to control articulation of the micro-mirrors relative to the substrate as the light source moves relative to the micro-mirrors and as the substrate moves relative to the light source.

Other aspects of the disclosed solar concentration system will become apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view, in section, of one aspect of the disclosed solar concentration system with micro-mirror array;

FIG. 2 is a top plan view, shown at magnification, of a portion of the micro-mirror array of the solar concentration system of FIG. 1;

FIG. 3A is a side elevational view of the micro-mirror array of FIG. 2, wherein the micro-mirror array is shown in a first configuration; and

FIG. 3B is a side elevational view of the micro-mirror array of FIG. 3A, wherein the micro-mirror array is shown in a second configuration.

DETAILED DESCRIPTION

As shown in FIG. 1, one aspect of the disclosed solar concentration system, generally designated 10, may include a receiver 12, a micro-mirror array 14 and a controller 16. The receiver 12 may be supported by a first support structure 18 and the micro-mirror array 14 may be supported by a second support structure 20. While the first and second support structures 18, 20 are shown as being separate structures, those skilled in the art will appreciate that the first and second support structures 18, 20 may be one and the same.

In one aspect, as shown in FIG. 1, the receiver 12 may be a photovoltaic receiver and may include one or more photovoltaic cells 22 and a lens 24. The photovoltaic cell 22 may be any photovoltaic cell capable of directly (or otherwise) converting light into electrical energy, such as a silicon-based solar cell, GaAs-based solar cell or the like. The lens 24 may focus harvested light, particularly light directed to the receiver 12 by the micro-mirror array 14, onto the photovoltaic cell 22. Additionally, the receiver 12 may include a heat sink (not shown) to assist in dissipating heat generated within the receiver 12. The heat sink 52 may be any device capable of dissipating heat from the photovoltaic cells 48, such as a finned heat sink, a heat pipe or the like.

In another aspect, the receiver 12 may be a solar thermal receiver. As used herein, “solar thermal receiver” is intended to include any device that collects solar energy to generate heat, regardless of the ultimate use of the heat. For example, a solar thermal receiver may include a fluid passing through an absorber tube onto which the solar energy is focused, thereby heating the fluid passing therethrough.

As shown in FIG. 2, the micro-mirror array 14 may include X rows and Y columns of micro-mirrors M mounted on a substrate 26. Those skilled in the art will appreciate that the configuration of micro-mirrors M in the array 14, as well as the number of micro-mirrors M in the array 14, may be varied without departing from the scope of the present disclosure.

In one aspect, the micro-mirrors M of the array 14 may be surfaces having a minimum reflectivity of about 80 percent and a minimum fill factor of about 80 percent. In one particular aspect, the array 14 may have a minimum packaging density of at least about 1000 micro-mirrors M per square foot of the substrate 26.

In another aspect, the micro-mirrors M of the array 14 may be 1 mm by 1 mm, aluminum-coated, single crystal silicon (SCS) micro-mirrors. The micro-mirrors M may be attached to a movable frame that is bonded with high temperature epoxy to pedestals to form a large angel piston/tilt beam steering system formed using complementary metal-oxide semiconductor (CMOS) and microelectromechanical systems (MEMS) (CMOS-MEMS). The movable piston/tilt mirror array may consist of more than 1,000 articulated mirrored surfaces per square foot with a fill factor of 95% or better and radius of curvature of greater than about 1.3 m.

As shown in FIGS. 3A and 3B, in one aspect, the micro-mirrors M may pivot relative to the substrate 26 in the x-y plane (i.e., in a pitching motion). The pivoting motion may range from at least about −10 degrees to at least about +10 degrees, though a greater range of motion is also contemplated. Therefore, the micro-mirrors M of the array 14 may have at least one degree of freedom relative to the substrate 26.

Furthermore, while not shown, those skilled in the art will appreciate that the micro-mirrors M may also pivot relative to the substrate 26 in the y-z plane (i.e., in a rolling motion). Therefore, in another aspect, the micro-mirrors M of the array 14 may have at least two degree of freedom relative to the substrate 26.

Still furthermore, those skilled in the art will appreciate that each micro-mirror M in the array 14 may be articulated independently of the other micro-mirrors M in the array. Alternatively, groups (e.g., rows or columns) of micro-mirrors M may be articulated independently of other groups of micro-mirrors M.

The substrate 26 may be a generally rigid structure that supports the array 14 of micro-mirrors M. Optionally, the substrate 26 may include a plurality of recesses (not shown) that receive the micro-mirrors M therein. The overall shape and geometry of the substrate 26 may be selected to optimize the redirection of light from the light source (e.g., the sun) to the receiver 12 and/or to optimize packaging efficiency (i.e., volume minimization). As one example, shown in FIG. 1, the substrate 26 may be formed as a parabolic disc or dish that receives the array 14 of micro-mirrors M on an inner concave surface thereof and focuses incoming light onto the receiver 12 (i.e., into a single point). As a second example, the substrate 26 may be formed as a parabolic trough that receives the array 14 of micro-mirrors M on an inner concave surface thereof and focuses incoming light into a line, thereby supplying concentrated light to a line of receivers 12. As a third example, the substrate 26 may be substantially flat, which may improve packaging.

The substrate 26 may be formed as a single piece or as an assembly of multiple pieces. Appropriate materials for forming the substrate 26 include steel and composite materials (e.g., moldable fiberglass), though various materials, including combinations of materials, capable of withstanding exposure to the elements may be used.

Referring back to FIG. 1, the solar concentration system 10 may include an optional window 28 that covers the micro-mirror array 14 to provide protection from the elements. The window 28 may be a generally planar sheet of transparent or partially transparent material. In one aspect, the window 28 may be formed from glass. In another aspect, the window 28 may be formed from a polymeric material, such as polycarbonate or acrylic. The transparency, flexibility and weatherability of the material (or materials) used to form the window 14 may be selected based upon design considerations.

While not shown in FIG. 1, those skilled in the art will appreciate that the window 28 may also enclose the receiver 12 within the volume defined by the substrate 26 and the window 28.

The controller 16 may be a processor, a computer or the like and may provide feed-back-type control signals to the micro-mirror array 14 to control the position (e.g., the pitch and roll angles) of the micro-mirrors M of the array 14 relative to the substrate 26 to focus incoming light onto the receiver 12 (see arrows A₁, A₂, A₃) as the sun (or other appropriate light/energy source) moves across the sky and/or as the platform supporting the system 10 moves relative to the sun.

Thus, by employing an array 14 of micro-mirrors M, the disclosed solar concentration system 10 maintains precise alignment with the sun without the need for a solar tracker, regardless of whether or not the substrate 26 is in motion, thereby substantially reducing the overall weight of the system 10 and reducing or eliminating reliability issues (e.g., the need for regular maintenance). Specifically, the micro-mirrors M articulate relative to the substrate 26, as opposed to articulating the entire substrate 26. However, optionally, the substrate 26 supporting the micro-mirrors M may also be articulated.

In an alternative aspect, the array 14 may be used to steer high energy lasers, such as airborne lasers. Beam steering control loops, usually called track loops, are critical components in adaptive optics systems, which compensate for wavefront distortion produced by the medium, such as turbulent atmosphere, through which the a laser beam propagates. A two-axis micro-mirror array in the beam path can be used to steer the beam to compensate for the atmospheric disturbances.

Although various aspects of the disclosed solar concentration system have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims. 

1. A solar concentration system comprising: at least one receiver; and an array of micro-mirrors connected to a substrate, each micro-mirror of said array being articulateable relative to said substrate.
 2. The solar concentration system of claim 1 wherein said receiver is positioned relative to said array such that said array directs incoming light from a light source to said receiver.
 3. The solar concentration system of claim 2 further comprising a controller configured to control articulation of said micro-mirrors relative to said substrate as said light source moves relative to said micro-mirrors and as said substrate moves relative to said light source.
 4. The solar concentration system of claim 1 wherein said receiver includes at least one photovoltaic cell.
 5. The solar concentration system of claim 1 wherein said receiver is a solar thermal receiver.
 6. The solar concentration system of claim 1 wherein said solar thermal receiver includes a fluid.
 7. The solar concentration system of claim 1 wherein said substrate includes a concave surface and said array of micro-mirrors is positioned on said concave surface.
 8. The solar concentration system of claim 1 wherein said substrate is shaped as a parabolic disc.
 9. The solar concentration system of claim 1 wherein said substrate is shaped as a parabolic trough.
 10. The solar concentration system of claim 1 wherein the substrate is flat.
 11. The solar concentration system of claim 1 wherein each micro-mirror of said array has at least one degree of freedom relative to said substrate.
 12. The solar concentration system of claim 1 wherein each micro-mirror of said array is configured to at least pitch and roll relative to said substrate.
 13. The solar concentration system of claim 1 further comprising a window connected to said substrate to form a substantially enclosed volume, wherein said array is positioned within said substantially enclosed volume.
 14. The solar concentration system of claim 1 wherein said substrate is essentially stationary relative to said receiver.
 15. The solar concentration system of claim 1 wherein said array includes at least 1000 of said micro-mirrors per square foot of said substrate.
 16. The solar concentration system of claim 3 further comprising a power supply configured to supply electrical energy to said array of micro-mirrors and said controller.
 17. A solar concentration system comprising: at least one receiver, said receiver including at least one photovoltaic cell; a substrate having a concave surface, wherein said substrate is essentially stationary relative to said receiver; and an array of micro-mirrors disposed on said concave surface, said array including at least 1000 of said micro-mirrors per square foot of said concave surface, wherein each micro-mirror of said array is articulateable relative to said substrate to direct incoming sunlight to said receiver.
 18. The solar concentration system of claim 17 further comprising a controller configured to control articulation of said micro-mirrors relative to said substrate.
 19. The solar concentration system of claim 17 further comprising a window connected to said substrate to form a substantially enclosed volume, wherein said array is positioned within said substantially enclosed volume.
 20. The solar concentration system of claim 17 wherein each micro-mirror of said array has at least two degrees of freedom relative to said substrate.
 21. A solar concentration system comprising: an array of micro-mirrors connected to a substrate, each micro-mirror of said array being articulateable relative to said substrate; at least one receiver, said receiver being positioned relative to said array such that said array directs incoming light from a light source to said receiver; and a controller configured to control articulation of said micro-mirrors relative to said substrate as said light source moves relative to said micro-mirrors and as said substrate moves relative to said light source. 